Immunostaining of tumour sections with antithyroglobulin antibody is helpful in confirming the follicular cell origin of the differentiated carcinomas, particularly in metastases of undetermined origin. Obtaining a positive reaction with anticalcitonin is now an essential step in the histological diagnosis of medullary carcinomas (Fig. 16.15). The majority of these tumours also give a positive immunoreaction with anticarcinoembryonic antigen.
Other immunoreactive peptides that are occasionally demonstrable include somatostatin, gastrin-releasing peptide (or its fragment, known as bombesin), adrenocorticotrophic hormone (ACTH), and corticotrophin-releasing hormone.
